1. Field of the Invention
The present invention relates to a shaping mold, an optical fiber guide block, processes for the production thereof and an optical fiber array. More specifically, it relates to a shaping mold for producing an optical fiber guide block which permits highly accurate positioning and fixing of all of a plurality of optical fibers, a process for the production thereof, an optical fiber guide block having the above excellent properties, a process for the production thereof, and an optical fiber array in which all of a plurality of optical fibers are highly accurately positioned and fixed in an optical fiber guide block.
2. Description of Related Art
For optically connecting a plurality of optical fibers to a plurality of optical fibers or connecting a plurality of optical fibers to one or a plurality of optical parts, it is desirable to carry out highly accurate pre-positioning and pre-fixing of each of optical fibers which are to be optically connected. For this purpose, many optical fiber guide blocks are used. An optical fiber guide block is a member for highly accurately pre-positioning and pre-fixing, for example, end portions of a plurality of optical fibers for optically connecting a plurality of the optical fibers to optical fibers or optical part(s).
The optical fiber guide block is a thin-sheet-shaped part having a predetermined number of optical fiber fitting portions formed on one surface thereof, which optical fiber fitting portions are used for positioning and fixing end portions of optical fibers. The optical fiber fitting portions are generally formed of grooves having a predetermined width and a predetermined depth each. The optical fiber guide block is largely classified into the following two types (1) and (2).
(1) An optical fiber guide block which is a thin-sheet-shaped member having a predetermined number of optical fiber fitting portions formed on one surface thereof, each optical fiber fitting portion extending from one side of the xe2x80x9cone surfacexe2x80x9d to the other side or from the one side to predetermined positions on the xe2x80x9cone surfacexe2x80x9d.
(2) An optical fiber guide block having an optical fiber fixing region where optical fiber fitting portions are formed on the upper surface thereof and a low-level region having its upper surface positioned at a lower level than the level of the upper surface of the optical fiber fixing region.
In the optical fiber guide block of the above type (2), a predetermined number of optical fiber fitting portions are formed on the upper surface of the optical fiber fixing region, and each optical fiber fitting portion extends from a side (boundary) between the optical fiber fixing region and the low-level region to the other side which is opposite to the boundary side and is on the upper surface of the optical fiber fixing region, or from the boundary side to a predetermined position on the above upper surface. The low-level region works as a setting on which the coating portion of coated optical fibers (optical fibers protected with a coating) such as an optical fiber tape is to be fixed.
Conventionally, attempts have been made to produce optical fiber guide blocks of the above types by an etching method or a cutting method, while attempts are being actively made to produce them by a mold-shaping method in recent years. The mold-shaping method is promising as a method capable of providing optical fiber guide blocks having high accuracy of an external form and high accuracy of optical fiber fitting portions and having high stability with regard to the above accuracy properties with high productivity at low costs.
When an optical fiber guide block having a plurality of optical fiber fitting portions is produced by a mold-shaping method, conventionally, there is used a shaping mold having transfer shaping surfaces which are used for shaping the above optical fiber fitting portions and upper surfaces around a region of the optical fiber fitting portions (the above upper surfaces will be referred to as xe2x80x9csided upper surfacesxe2x80x9d hereinafter). The above conventional shaping mold has a cross section, for example, as shown in FIG. 11(a). FIG. 11(a) is a schematic cross-sectional view of one example of conventional shaping molds. A shaping mold 80 shown in FIG. 11(a) has convex portions 81 for shaping a predetermined number of optical fiber fitting portions, and bottoms between adjacent convex portions 81 are at the same level as the level of shaping surfaces 82a and 82b to be used for shaping the sided upper surfaces (for example, see FIG. 4 of JP-A-8-292332).
When the above shaping mold 80 is used, an optical fiber guide block shown in FIG. 11(b) is obtained. FIG. 11(b) shows a schematic cross-sectional view of an optical fiber guide block 88 obtained by means of the shaping mold shown in FIG. 11(a). The optical fiber guide block 88 has a structure in which peak surfaces 86 present in boundaries between adjacent optical fiber fitting portions are substantially at the same level as the level of sided upper surfaces 87a and 87b. 
Meanwhile, for complying with an increased density of an optical circuit, etc., in recent years, there is increasingly demanded an optical fiber array in which a plurality of optical fibers are positioned and fixed at intervals which are as close as possible. The above optical fiber array has an optical fiber guide block, a plurality of optical fibers positioned and fixed on the optical fiber guide block and a pressing member used for pressing and fixing the optical fibers to optical fiber fitting portions. With the above increasing demand, it is also increasingly demanded to form optical fiber fitting portions at intervals as close as possible in an optical fiber guide block for constituting the above optical fiber array.
As the pitch of a plurality of optical fiber fitting portions is decreased when the optical fiber fitting portions are formed, theoretically, there can be produced an optical fiber guide block which permits positioning and fixing of a predetermined number of the optical fibers in a state where circumferential surfaces of optical fibers located side by side are in contact with each other. When the circumferential surfaces of adjacent optical fibers are in contact with each other, however, there is no lubricity caused between the circumferential surfaces of the adjacent optical fibers, and it is therefore difficult to position and fix the optical fibers. Practically, therefore, it is desirable to give a gap of approximately several xcexcm between the circumferential surfaces of the adjacent optical fibers.
When a plurality of optical fibers are positioned and fixed in a state where the circumferential surfaces of adjacent optical fibers are in contact with each other or in a state where the circumferential surfaces of adjacent optical fibers are apart from each other by the above gap of several xcexcm, and when the peaks of boundary portions between the adjacent optical fiber fitting portions are substantially at the same level as the level of the sided upper surfaces, the amount of projection of the circumferential surfaces of the optical fibers (height of projected portions) measured from the level of the sided upper surfaces is large.
When an optical fiber array is produced by fitting a plurality of optical fibers in optical fiber fitting portions and pressing and fixing the optical fibers with a pressing member, therefore, there is formed a large gap between the optical fiber guide block and the pressing member, and an adhesive layer formed in the gap therefore has a large thickness. As a result, the adhesive layer is liable to peel off due to curing contraction or due to swelling caused by the absorption of water, which causes a problem that the reliability of the optical fiber array decreases. Further, each of optical fiber supporting positions of the optical fiber fitting portions is considerably low. That is, when cross sections of each optical fiber fitting portion and each optical fiber are taken in the direction perpendicular to the length direction thereof, the position of each of contact portions of the optical fiber fitting portions and the circumferential surfaces of the optical fibers is considerably lower than the center (optical axis) of each optical fiber, which causes a problem that the stability of the optical fibers which are once positioned is low.
The present inventors already found that when an optical fiber array comprising an optical fiber guide block, optical fibers and a pressing member which are fixed with an adhesive is produced, the above problems can be overcome by an optical fiber guide block having optical fiber fitting portions having a specific form shaped by cutting with one blade made of diamond (see JP-A-6-289236, particularly, FIG. 5(c) in the publication).
That is, it was found that the above problems can be overcome by an optical fiber array 95 shown in FIG. 12 (schematic front view of an optical fiber array). Specifically, the optical fiber array 95 is structured by providing an optical fiber guide block 92 having a predetermined number (for example, 4 in FIG. 12) of optical fiber fitting portions 91a to 91d in which peak surfaces of boundaries between adjacent optical fiber fitting portions are at a level lower than the level of the sided upper surfaces 90a and 90b and which optical fiber fitting portions 91a to 91d are formed by cutting with one diamond blade, fitting optical fibers 93a to 93d in the optical fiber fitting portions 91a to 91d and pressing and fixing the optical fibers 93a to 93d with an adhesive (not shown) and with a pressing member 94.
As already described, attempts are being actively made to produce optical fiber guide blocks by a mold shaping method in recent years. The optical fiber guide block having the above specific structure can be also produced by a mold shaping method. When the optical fiber guide block having the above specific structure is produced by a mold shaping method, generally, (1) the peak surface of each boundary between optical fiber fitting portions is easily rounded, and (2) the bottom of each optical fiber fitting portion is easily formed as an edge of two surfaces (inner surfaces of each optical fiber fitting portion), as compared with a case where a predetermined number of optical fiber fitting portion are formed by cutting.
For producing an optical fiber guide block by a mold shaping method, it is required to prepare a shaping mold having transfer shaping surfaces for shaping optical fiber fitting portions and sided upper surfaces (the mold having transfer shaping surfaces for shaping optical fiber fitting portions and sided upper surfaces will be referred to as xe2x80x9cshaping mold Ixe2x80x9d hereinafter). For producing an optical fiber guide block having the above specific form, the shaping mold I (for example, FIG. 13 shows 4 convex portions for shaping optical fiber fitting portions, while the number of the convex portions shall not be limited to 4) can be relatively easily prepared by processing a flat-plate-shaped or block-shaped mold material with a double tapered grinder and a flat grinder according to steps shown in FIGS. 13(a) to 13(c).
FIGS. 13(a) to 13(c) show steps of preparing a shaping mold with one grinder with a view to attaining high productivity. FIG. 13(a) is a schematic front view of a mold material, etc., at the step of forming convex portions designed for shaping optical fiber fitting portions, FIG. 13(b) is a schematic front view of a mold material, etc., at the step of forming a circumferential region, and FIG. 13(c) is a schematic front view of a shaping mold obtained.
Specifically, as shown in FIG. 13(a), three grooves 103a, 103b and 103c are formed in one surface 101a of a mold material 101 with a double tapered grinder 102. The grooves 103a, 103b and 103c are substantially equivalent in depth. A boundary portion between the adjacent grooves 103a and 103b constitutes a convex portion 104a designed for shaping an optical fiber fitting portion, and a boundary portion between the adjacent grooves 103b and 103c constitutes a convex portion 104b designed for shaping an optical fiber fitting portion. In FIG. 13(a), a chain line C10 shows an outer side surface of a convex portion 104c to be formed later (for shaping an optical fiber fitting portion), and a chain line C11 shows an outer side surface of a convex portion 104d to be formed later (for shaping an optical fiber fitting portion).
Then, as shown in FIG. 13(b), the convex portion 104c for shaping an optical fiber fitting portion is formed outside the groove 103a which is located in the leftmost position when the mold material 101 is viewed in the length direction of the grooves 103a to 103c, and the convex portion 104d for shaping an optical fiber fitting portion is formed outside the groove 103c which is located in the rightmost position. That is, a groove having a predetermined depth is formed in a region 105a outside a portion which is to constitute the convex portion 104c, and a groove having a predetermined depth is formed in a region 105b outside a portion which is to constitute the convex portion 104d, with the above double tapered grinder 102.
The convex portions 104a to 104d designed for shaping optical fiber fitting portions are positioned on the upper surface side of an elevated region 106 having a predetermined thickness. When the above last two grooves are formed in the outside regions 105a and 105b, the double tapered grinder 102 is allowed to grind into the mold material 101 sufficiently deep so that the left-side surface of the convex portion 104c positioned in the leftmost position forms a substantially continuous surface with an upper surface of a region on the left side of the elevated region 106 and that the right-side surface of the convex portion 104d positioned in the rightmost position forms a substantially continuous surface with an upper surface of a region on the right side of the elevated region 106.
Then, remaining portions of the above regions 105a and 105b are removed with a flat grinder (not shown), to obtain a shaping mold shown in FIG. 13(c).
As described above, the convex portions 104a to 104d are formed, and the regions 105a and 105b outside the convex portions 104a to 104d are removed, whereby a shaping mold 108 (shown in FIG. 13(c)) can be relatively easily prepared. And, an optical fiber guide block having the above specific form can be obtained by a mold shaping method using the shaping mold 108 as a shaping mold I.
In FIG. 13(b), a chain line C12 shows a position of upper surface of the circumferential region to be formed by removing the above outside region 105a, and a chain line C13 shows positions of upper surface of the circumferential region to be formed by removing the above outside region 105b and a side surface of the elevated region 106 on the circumferential region side. In FIG. 13(c), 107a and 107b show upper surfaces of the circumferential regions, and the upper surfaces 107a and 107b work as shaping surfaces for transfer-shaping the sided upper surfaces of an optical fiber guide block.
However, when evaluated on the basis of a positioning accuracy of a plurality of optical fibers, an optical fiber guide block produced by a mold shaping method sing the above-prepared shaping mold is not satisfactory in form accuracy, since the grinder is allowed to grind into a mold material deeper for forming the left-side side surface the leftmost convex portion and the right-side side surface of the rightmost convex portion.
For example, in the shaping mold 108 shown in FIG. 13(c), left-side side surfaces of the convex portions 104a, 104b and 104d are formed by grinding with a substantially the same region of the double tapered grinder 102 during the grinding, and these left-side side surfaces are found to have substantially the same form when evaluated on the above basis. Since, however, the left-side side surface of the convex portion 104c is formed by grinding with a clearly different grinding surface of the double tapered grinder 102 during the grinding, the above left-side side surface of the convex portion 104c is found in many cases to constitute no xe2x80x9csubstantially the same formxe2x80x9d when evaluated on the above basis. Similarly, right-side side surfaces of the convex portions 104a, 104b and 104c are found to have substantially the same form when evaluated on the above basis, while the right-side side surface of the convex portion 104d is found in many cases to constitute no xe2x80x9csubstantially the same formxe2x80x9d as the form of the above right-side side surfaces of the convex portions 104a, 104b and 104c when evaluated on the above basis.
For example, the optical fiber guide block 92 shown in FIG. 12 is formed by a mold shaping method using the above shaping mold 108, and optical fibers 93a, 93b, 93c and 93d are fitted in the optical fiber fitting portions 91a, 91b, 91c and 91d of the optical fiber guide block 92. In this case, of support positions P13 and P14 of the optical fiber fitting portion 91B for the optical fiber 93b and support positions P15 and P16 of the optical fiber fitting portion 91c for the optical fiber 93c, the support positions P13 and P15 are on one level, and the support positions P14 and P16 are also on one level. However, the above support positions P13 and P15 are on one level, and a support position P11 of the optical fiber fitting portion 91a for the optical fiber 93a and a support position P17 of the optical fiber fitting portion 91d for the optical fiber 93d are on another (different) level in many cases. Similarly, the above support positions P14 and P16 on one leve, but a support position P12 of the optical fiber fitting portion 91a for the optical fiber 93a and a support position P18 of the optical fiber fitting portion 91d for the optical fiber 93d are on another (different) level in many cases.
As a result, when an optical fiber array 95 (see FIG. 12) is produced by fixing and pressing the optical fibers 93a to 93d to the optical fiber fitting portions of the optical fiber guide block 92 with a pressing member 94 (see FIG. 12) and with an adhesive, (1) the height (position of optical axis) of the optical fibers 93b and 93c from the level of a predetermined reference surface (e.g., sided upper surfaces 90a and 90b of the optical fiber guide block 92) differs from the height of the optical fibers 93a and 93d, or (2) the pitch between the optical fiber 93b and the optical fiber 93c differs from the pitch between the optical fiber 93a and the optical fiber 93b or from the pitch between the optical fiber 93c and the optical fiber 93d. It is therefore difficult in many cases to carry out highly accurate positioning and fixing of all of these optical fibers 93a to 93d. 
Under the circumstances, it is a first object of the present invention to provide a shaping mold for producing an optical fiber guide block which permits highly accurate positioning and fixing of all of a plurality of optical fibers.
It is a second object of the present invention to provide a process for the production of the above shaping mold.
It is a third object of the present invention to provide an optical fiber guide block having the above excellent properties.
It is a fourth object of the present invention to provide a process for the production of the above optical fiber guide block.
It is a fifth object of the present invention to provide an optical fiber array comprising an optical fiber guide block which permits highly accurate positioning and fixing of all of a plurality of optical fibers.
For achieving the above objects, the present inventors have made diligent studies and have found the following. The above first and second objects can be achieved by a shaping mold of which the circumferential regions have their boundaries with the elevated region at a level lower than the level of bottoms of grooves formed between one convex portion and another convex portion of convex portions designed for shaping optical fiber fitting portions and of which the elevated region has additional side surface(s) different from side surfaces of the convex portions. The additional side surface refers to a side surface indicated, for example, by reference numeral F3 in FIG. 3. Further, the above third and fourth objects can be achieved by mold-shaping a shapeable material into an optical fiber guide block having a predetermined structure with the above shaping mold.
Further, the above fifth object can be achieved by an optical fiber array comprising the above optical fiber guide block having a plurality of optical fiber fitting portions, and optical fibers pressed and fixed to the optical fiber fitting portions with a pressing member, at least the optical fiber guide block and the pressing member being fixed with an adhesive.
The present invention has been completed on the basis of the above findings.
That is, according to the present invention, the above first object is achieved by a shaping mold having transfer shaping surfaces for producing an optical fiber guide block having a plurality of optical fiber fitting portions in the form of grooves and side portions in the vicinities of a region where the optical fiber fitting portions are formed, the shaping mold comprising an elevated region and circumferential regions adjacent to the elevated region, the elevated region having a plurality of convex portions designed for shaping the optical fiber fitting portions and having side surfaces forming boundaries with circumferential regions, one boundary being present between one of said side surfaces and one circumferential region, the other boundary being present between the other of said side surfaces and the other circumferential region, the boundaries being positioned at a level or levels lower than the level of bottoms of grooves formed between one convex portion and another convex portion, said side surfaces being additional side surfaces different from side surfaces of any convex portions.
According to the present invention, the above second object is achieved by a process for the production of a shaping mold having transfer shaping surfaces for producing an optical fiber guide block having a plurality of optical fiber fitting portions in the form of grooves and side portions in the vicinities of a region where the optical fiber fitting portions are formed, the process comprising the steps of
forming a plurality of convex portions in a mold material, the convex portions being designed for transfer-shaping the optical fiber fitting portions, and
forming circumferential regions in the mold material,
the step of forming the circumferential regions including the formation of side surfaces of an elevated region, which side surfaces are additional side surfaces different from side surfaces of any convex portions,
the step of forming the circumferential regions further including the formation of boundaries one of which is present between one of the side surfaces of the elevated region and one circumferential region and the other is present between the other of the side surfaces of the elevated region and the other circumferential region, at a level or levels lower than the level of bottoms of grooves formed between one convex portion and another convex portion.
According to the present invention, the above third object is achieved by an optical fiber guide block comprising a region of a plurality of optical fiber fitting portions formed in one surface in the form of grooves and side regions adjacent to the region of the optical fiber fitting portions, the optical fiber guide block being formed by a mold-shaping method, the optical fiber fitting portions having boundaries between one optical fiber fitting portion and another optical fiber fitting portion, the boundaries having peaks or peak surfaces at a level lower than the level or levels of side region edges on the sides of the region of the optical fiber fitting portions, the side regions having additional side surfaces which are different from any optical-fiber-supporting side surfaces of the optical fiber fitting portions and which are on the side of the region of the optical fiber fitting portions. The xe2x80x9cside region edgexe2x80x9d refers, for example, to an edge of a sided upper surface 22a or 22b (horizontal surface) which is on the right side of the left xe2x80x9csided upper surfacexe2x80x9d or on the left side of the right xe2x80x9csided upper surfacexe2x80x9d in FIG. 4.
According to the present invention, the above fourth object of the present invention is achieved by a process for the production of an optical fiber guide block comprising a region of a plurality of optical fiber fitting portions in the form of grooves and side regions adjacent to the region of the optical fiber fitting portions by a mold shaping method,
the process comprising providing the above shaping mold and mold-shaping a shapeable material into the optical fiber guide block with the shaping mold.
According to the present invention, the above fifth object of the present invention is achieved by an optical fiber array comprising the above optical fiber guide block, a predetermined number of optical fibers fitted in optical fiber fitting portions of the optical fiber guide block and a pressing member used for pressing and fixing the optical fibers to the optical fiber fitting portions, at least the optical fiber guide block and the pressing member being bonded and fixed to each other.